The invention relates to a method and an apparatus for cleaning the filters in filtering boxes associated with machines and machine rooms and the like. The filtering box contains a filter and a suction mechanism aspirating air to be cleaned through the filter. For the purposes of cleaning the filter periodically, the apparatus contains a second air transport device which is capable of aspirating air from the region of the box adjacent the clean side of the filter and through the filter, thus carrying along any contaminations or dirt which had accumulated on the impure side of the filter during normal operation. The apparatus is so constructed that, during the cleaning of the filter, the impure air is continuously admitted to the apparatus and is aspirated by the second air transport mechanism. Part of the air aspirated by the first air transporter is returned and blown out of the filter.
In a known process and apparatus of this type, a supplementary air stream was admitted to the filtering box adjacent the clean side of the filter. This additional air was taken from ambient atmospheric air via inlet channels which originated in the outlet apertures of the filter box and were capable of being blocked by suitable mechanisms. This previously known apparatus has the inherent disadvantage that, during the cleaning operation of the filter, the clean side of the filter was subject to contamination by any dirt or impurities carried by the supplementary air stream and these contaminations now deposited on the clean side of the filter would then be blown out in concentrated form at the onset of normal suction operation via the normal outlet openings of the filter.